I. Respiration: This project will extend the present studies of the interactions between groups of medullary respiratory neurones, with emphasis on nucleus of the solitary tract - nucleus retroambigualis interactions. The object is to understand how the medullary respiratory pattern is generated. Correlations between simultaneously recorded extracellular spike trains, correlations between spike trains and intracellularly recorded post-synaptic potentials, antidromic mapping and latency analysis will be used to characterize these interactions. The cells in the spinal cord receiving nucleus of the solitary tract projections will be identified, and the function of this pathway will be differentiated from that of the descending projections of the cells of nucleus retroambigualis. II. Ineffective synapses: This project will be undertaken concurrently with the above study. It will attempt to determine, using conventional extracellular techniques, how the receptive fields in lamina IV dorsal horn cells develop in kittens; whether ineffective synapses play a part in this development, and whether ineffective synapses differ from those in mature animals. Experiments in adult animals will determine the nature of the mechanism governing the "ineffectiveness". Other experiments utilizing simultaneous extracellular recordings and averaging will attempt to identify the origin of the small impulses recorded in substantia gelatinosa, and determine whether these are implicated in the ineffective synapse mechanism.